A brake system is a device or mechanism for applying frictional resistance to the motion of a body and thereby absorbing mechanical energy by transferring it into heat. This will slow down a vehicle or make it stop.
If a driver presses a brake treadle, a hydraulic generator generates hydraulic pressure that is supplied to a brake shoe. The brake shoe presses a brake drum or a brake disk by an operation of the hydraulic pressure, and thereby decelerates speed of a vehicle.
However, a vehicle with the conventional brake system decelerates or stops only by an operation of a brake drum or a brake disk attached to a wheel. Therefore, it is unsuitable while running at high speed and its braking performance is low.
In order to avoid the above problems, a driver applies a so-called engine brake technique. That is, a driver rapidly changes a speed level from a high-speed level to a low-speed level to decrease a speed of a vehicle at the high speed.
However, it is difficult for a driver to operate the speed change lever from a high-speed level to a low-speed level during urgent circumstances. Furthermore, a braking performance is low in this case.